You cut out the part where they literally told Qui Gon to investigate it further and that they’re going to help, does that count as “pondering the possibility?”
With no real assistance or back up. I think it’s a bit more generous read of them, to me, that they simply refused to accept the notion but wanted to find out anyway just in case. But like I said, being arrogant, for me, doesn’t mean they’d be entirely bullheaded or overly pompous.
They actually care a lot. I found the IMDB transcript.
“Ki-Adi-Mundi: Impossible. The Sith have been extinct for a millennium.
Mace Windu: I do not believe the Sith could have returned without us knowing.
Yoda: Ah, hard to see the dark side is.
Mace Windu: We will use all our resources to unravel this mystery. We will discover the identity of your attacker. May the Force be with you.”
This isn’t refusing to accept it. Yoda in effect says “maybe we missed something,” then Mace says they’re going to use ALL their resources on it.
Why don’t they? Presumably Qui Gon and Obi Wan have their fight with Maul before the council’s resources would matter, which would make sense because that’s only in like a few days, if that, and the Sith have been in hiding a thousand years. Maybe they could have sent more Jedi in case Maul came out of hiding, but they didn’t want to destabilize the political situation further by making it look like the Jedi were Naboo’s private army. Of course a lot of viewers criticize them for that kind of thing too, but that’s the opposite of arrogance, if anything it’s the refusal to assert themselves.
Why don’t we get any follow up on it and what they’re doing to look for the other Sith? Ask Lucas on that one. Maybe something else completely offscreen that went nowhere. That’s why I’m criticizing the script and lack of continuity between the movies, instead of saying this was the Jedi being “arrogant.” They’re being dumb, not proud.